Recently, demand for secondary batteries as an energy source has become rapidly growing. Among the secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life and low self discharge rate have been commercialized and widely used.
Although graphite is mainly used as an anode material of the lithium secondary battery, it is difficult to increase the capacity of the lithium secondary battery, since the capacity per unit mass of the graphite is as small as 372 mAh/g. Accordingly, an anode material for forming an intermetallic compound with lithium, such as silicon, tin and oxides thereof, has been developed and used as a non-carbon anode material having an energy density higher than that of graphite in order to increase the capacity of the lithium secondary battery. However, although the non-carbon anode material has high capacity, an initial efficiency is low, which causes a large lithium consumption during the initial charge-discharge, and a large irreversible capacity loss.
In the related arts, a method of overcoming the irreversible capacity loss of the anode using a material which can provide a lithium ion source or a storage material to the cathode material and which exhibits electrochemical activity after the first cycle so as not to deteriorate the performance of the entire battery has been studied and proposed. For instance, an oxide containing an excessive amount of lithium such as Li6CoO4 has been applied as a sacrificial cathode material or an irreversible additive (or an overdischarge-preventing agent) to the cathode.
However, when the irreversible additive is used, the capacity characteristics of the cathode may be insufficient. Therefore, even when the irreversible additive is used, further improvement in the capacity characteristics of the cathode and the lithium secondary battery including the same may be required.